Pipe systems for underground gas and water distribution are assembled and fused in-situ. Changes in direction are common in underground installations. Minor changes can be accommodated by the inherent flexibility of the pipe, while major changes are currently effected by a range of molded or formed fixed angle bends. The molded or formed bends are fused into the system to maintain a consistent and fully sealed system.
One form of existing bend involves cutting two pipe ends at the same angle and fusing two such cuts together. This forms an angle that is twice the cut angle of each pipe end, providing a mitred joint. Bends fabricated by this angle cut and butt fuse process tend not to have good flow characteristics and they are considered not to have the same strength as the pipe system from which they are formed.
In many situations the molded fixed angle bends do not provide the appropriate degree of directional change. In this situation several bends must be assembled together or extra strain must be placed on the pipe and jointing to accommodate the change in direction. These factors make it difficult to complete the system without resorting to alternative materials which involve transitions and often non-fused elements.
An adjustable bend that could be set at the required angle and then fused would provide benefits in that it would enable fewer components to be used, it would reduce the strain on other components and it would maintain a consistent and fully fused system.
To maintain the flow properties of the pipe system it is also important that a large loss in pressure head does not occur as the fluid flows through the bend. To avoid a significant loss in pressure the adjustable bend must create a smooth change in direction and provide a consistent bore profile at whatever angle it is set.
An objective of the invention is to form an adjustable bend which may be made, for example, in medium density polyethylene (MPDE) which can be readily set to the required angle during installation, the relatively movable parts being then fusable to complete a low pressure loss bend of the required angle, which may then form part of a fully fusion sealed pipe system.